It actually occurs through the transformation of a neutron into a proton or
vice versa through what is called "the Weak Nuclear Force" or "Weak
Interaction". This process has proved to be a relative of Electromagnetism
although it is a far weaker force than that ( though still stronger than Gravity
).

The process is ESSENTIAL in the formation of elements in stars and so in the
existence of stars! ( The process allows neutron formation from protons. )

When we look at the lighter elements, those off the line of "stability"
tend to decay via beta.

Those elements with "too many neutrons" decay by electron emission
( beta-negative ) while those with "inadequate" neutrons decay by
beta-positive emission - so called "positrons" or "antimatter
electrons". ( The latter decay is used in the medical scans called
PET scans - Positron-Electron Tomography. ) An example of the latter is

Gamma emission can also take place after beta emission although no spectral
lines are emitted in this range.

With this emission comes one of the strangest of all
subatomic particles - the NEUTRINO , n , or
neutral little one ( Click
for excellent reference )

This critter is only slowly being understood. There are three, associated with
the electron, the muon and the tauon ( which are more massive versions of the
electron ) with corresponding "anti matter" variants. It is very elusive
but one detector has been "watching" those from the Sun's core for
over 35 years. It takes about 2 million km of Pb to stop half of those coming
from the Sun! They are passing through all of us at an enormous rate of at least
millions each second, but doing no damage.

They have no charge,

they have "spin" ( or "polarization" or "angular
momentum", )

they have just been shown to have mass ~ about 1/100 000 th the mass of
an electron!

they have momentum

they are strongly suspected of changing identity as they progress.

Detectors all watched neutrinos arrive from the supernova in the Magellenic
Cloud of 1987 - a wonderful feat! ( Ref
1 )